Steel is the material that is being used in various industries such as for automobiles, home appliances, and construction thanks to its excellent physical properties. However, since the steel easily reacts with oxygen to cause corrosion, it is essential to perform a surface treatment such as protective layer coating in order to protect against such corrosion.
The steel is processed in various forms such as sheets, rods, and tubes, and a thin steel sheet is one of the most common types of steel products used in the industry. As a method most commonly used to prevent corrosion of the steel sheet, a metal passivation film having higher reactivity with oxygen than iron is coated on a surface of the steel sheet, thereby serving as a sacrificial anode. As a result, the corrosion of the steel sheet is delayed.
Typical examples of the metal employed for such coating of the steel sheet may include zinc and aluminum, and examples of a method of coating such a metal on the steel sheet may include hot dipping and electroplating. Currently, the plating method is being used for most steel sheet surface treatments since it is easy and inexpensive.
When the steel sheet is coated by using a zinc plating method, it can be considered to increase a coating weight of zinc in order to improve corrosion resistance of the steel sheet. However, a method for improving the coating weight of zinc by reducing a plating rate is employed, but this method causes productivity deterioration.
Further, an increase in the coating weight of zinc involves an increase in the weight of the steel sheet with zinc. Accordingly, in the case of transport equipment, the weight increase leads to reduction in fuel consumption efficiency. In addition, natural resources of zinc has been rapidly decreased in recent years, so it is urgently required to discover materials that can replace zinc.
As part of this attempt, a method has been being developed to improve the coating weight of the zinc-plating steel sheet by adding a different kind of element without increasing the coating weight of zinc. Examples of the different kind of element may include aluminum and magnesium.